Telephone installation



5. POHLMANN ET AL.

Nov. 16 1926.

' TELEPHONE INSTALLAIION Filed July 15 1921 2 Sheets-Sheet 1 w gm M- mmf Nov. 16 1926. 1,606,805

' B. POHLMANN ET AL TELEPHONE INS TALLATION Filed July 15, 1921 2 Sheets-Sheet 2 Patented Nov. 16, 1926.;

UNITED STATES v 1,606,805 PATENT ori ice.

BRUNO POHLMANN, OF SIEMENSSTiADT. NEAR BERLIN, AND. ARTHUR CLAUSING, 0F

BERLIN-CHARLOTTENBJJ'RG, GERMANY, ASSIGNORS TO SIEMENS HALSK E, AK- TIENGESELLSCHAFT, 0F SIEMENSSTADT, 'NEAR BERLIN, GERMANY, A CORPORA- TION OF GERMANY.

Application filed July 15. 1921. Serial No. 584,949, and in Germany October 31, 1919.

' Our invention relates to telephone installations and more especially toan amplifying connection for use in installations. lVe. are aware that such connections have already been proposed in which a device serving to ampl-ifythe speaking currentis arranged within the line, always one for each speaking direction, andwhich moreover are adapted to be interconnectedfor the speaking direction req'uiredby means of switch relays in such a manner that for the duration of a conversation always only the amplifier appertaining to the speaking direction entering into consideration for the time being will be interconnected. As the speaking direction changes there likewise takes place a change of the amplifier interpolated into'the line. For the purpose of controlling the switch relays use is made of'alten nating current relays (oscillation relays) which are arranged within the battery circuits of the switch relays and which are controlled by the speaking currents in such a manner that they will eitherclose or. open the cir uit of the relay to be actuated, according to the method of connection pro- Y vided.

-next following word will be-lost.

However, the drawback involved in the use of switch. relays of the aforesaiddescrip tion resides invarious mechanical switch operations taking place successively before .the spoken words are able to pass from the one section of the .line into the other. The result is that in general after every break in the conversation the first syllable of the This drawback evidences itself in a particularly annoying manner whenever a plurality of amplifying connections of the said kind are inserted in the line. In addition, o'scilla-' 'tion relays require an exceptionally care- .ful watching and adjust-men The aforesaid defects caused as aforesaid by the mechanical switch operations are remedied in accordance with our'invention by reducing the number of the switch relays oreven eliminating these latter entirely, by I not subsequently interconnecting. the amplifiers by mechanical switch operations intd the line, but by arranging them in the line permanently, whereby 'they are ,nnegely adapted to be-alternately brought into the operative position by fluctuations of the TELEPHONE INSTALLATION.

grid potential created bv rushes of current,

' whereas when they are in a state of rest the purpose of operating the amplifiersthere are arranged in accordance with our invention for each speaking direction a ready-working directing amplifier which is adaptedto interconnect by means of the speaking currents arriving from the respective direction, the

working voltage into the grid circuit of the v appropriate speech amplifier,while simultaneously rendering the other directing amplifier appertaining to the opposite speaking direction inoperative by potential displacement in front of its grid.

The control of the speech amplifier is effected by the potential difference, obtained through the drop of voltage on the'part of the anode currentof the directing amplifier along a resistance inserted in the anode current. In order to secure only gradual fluctuations of voltage of slight amplitude' at the grid of the speech amplifier there is connected, in accordance with our invention, a suitable compensating condenser in parallel with the resistance. The reversing speaking currents; are preferably aniplified before passing into. the directing amplifier,

in which case the'degree of amplification and the compensating'condenser are so, dimensioned that the directing amplifier will permanently produce a displacement of potential. at which the speech amplifier will operate within the linear amplifying area. We have found it to be of advantage to render the control voltage, derived from the anode circuit of the directing amplifier, adjustable in order to be able to adapt it to any difference in the tubes when replacing these latter. w

Having regard-to the fact that during a conversation the individual words transmitted supply the control device. with alternating currents of varying amplitude, the possibility exists that the vdirecting amplier in accordance with the varying intensity of the control currents, might produce different displacements of potential which again might under certain circumstances cause a distortion of speech. 'Such a distortion will, however not arise When the displacement of potential fluctuates slowly for a time and only to such an extent that the speaking waves at the speech amplifier Willalways be disposed within the range'ofthe linear portion of the amplifying characteristic (characteristic of the grid voltageanode current). The feature of causing only momentarily slow fluctuations to arise is realized by the compensating condenser. Besides, in order to render the displacement of' potential independent of the strength of the speaking currents, we have found it expedient to operate the directing amplifier permanently With saturation current, i. e. to so select the preliminary amplifying devices 1 that the same amplifying currents will be present both for the feebler speaking currents as Well as for the more powerful ones. Now it has been discovered that even in the case of such systems of electric connection Where no mechanical control relay is made use of, there will still he lost certain portions of the first syllables of .words transmitted when a change in the direction of the conversation-occurs and it has further been found that this defect is attributable to a rise in the drop of voltage at the control resistance. .The cause forthis must be sought in the fact that the condenser connected in parallel to the control resistance will, when not charged, offer only a slight resistance to thecur-ent impulses at the commencement of'a Wave train. In fact the .condenser practically short-circuits the resistance so that as a result the drop of voltage cannot fully develop.

Now this defect is remedied in accordance With our invention by replacing the condenser by an oscillating element composed of capacity and induction tuned to thefrefications of an amplifying connection em-v bodying our invention are illustrated in a purely diagrammatic manner by way of example. In the drawings- Fig. 1 discloses an amplifying connection provided with a set of amplifiers for each line section, and

Figs. 2 to '6 disclose different systems'of connection adapted to prevent the loss ofthe first syllablesin the transmission of the voice after a break in the conversation.

Referring to Fig. 1, there are arranged in the section F of a long-distance line a speech amplifier R and a directing ampli-.

fier R,, an additional amplifying device R7 being inserted in front of this latter.

The said section of the long-distance line is inductively coupled by means of a pre-trans lator V to the speech amplifier R and by a pre-translator V to the amplifier R Within the anode circuit of the directing amplifier there is located a resistance W with which a condenser C is connectedup in parallel. For the long-distance line section F there are provided glow cathode tubes R Rf R correspondingly arranged in exactly the same manner as those in the case of line section; F,. To the ends of re- 'sistance IV within the anode circuit of the "directing amplifierR' are connected the grid circuits of the speech amplifier R and of the set of directing amplifiers R' R" In a similar manner the grid circuits of the speech amplifiers R and of the set of directing amplifiers R,',, R, are connected up to" the ends of the resistance In the place of a plurality of individual batteries, use is made as'far as practicable of common batteries for the several amplifying tubes. The manner of operation of the abovedescribed ain' lows;

The speaking currents arriving across the long-distanceline F flow, on theone hand, into the amplifierR and, on the other hand, into the set of amplifiers R,, R',. "The speech'amplifier R is,. however,'at this juncture inoperative and passes the iii-coining speaking currents on after powerfully damping them. On the other hand, the speaking currents are powerfully amplified .within the set of directing amplifiers, while within the anode circuit thereof there is produced a diminution of 'the'pulsations pf the pul-' sating continuous current by'the condenser G and WVlll'Oli continuous current brings about a change in the'drop of voltage at the ends of the resistance-IV causing such a displacement of potential to take place at the grid of the speech amplifier R that this latter will now become operative and Willbegin to function Within the linear amplifying area. Resistance W is preferably arranged -to be adjustable, so that on replifying connection is as 'fol placing or renewing the rectifier, the redrop. The duly amplified speaking current is transmittedby the directing amplifier R, to the long-distance line section FQ. The voltage drop at the resistance at the same time causes a displacement of potential at the grids of R' 'R and by these means sistance maybe adjusted to the same voltage For if'such a contingency should arise the result would bethat disturbances (howling) would arise'w'ithin the speech amplifiers connected. in series and now in'readiness to 8 operate, owing to re-coupling.

As soon as the subscriber connected up to the long-distance line section F stops talking, the condition of the several'por- -tions of the circuit returns to normal while now the subscriber .connected up to line section F is in his turn enabled to transmit a communication across the speech'amplifier R into the long distance line section F,. in the very same manneras the sub-' scriber connected up to line sectionF hadpreviously done.

However, instead of employing directly the potential differences prevailing at the resistances \V, and W a relay may be intel-connected into the anode circuit of the directing amplifier adapted to apply a suit-,

able battery to the grid circuits entering into consideration.

- The -directingamplifiers need not be ar- '25 ranged at the same place, as the speech amplifiers. Under certain conditions it may. even prove expedient in order to reduce the influence of disturbing currents to arrange the control elements (R',, IV, and R,, R

respectively) appertaining to the two subtions. 1

In Figs. 2 to 6 there are disclosed several systems of connections adapted to prevent the loss of the first syllables in the trans-.

mission of the voice .aftera break in the conversation.

In the form of connection; disclosed in scribers in the vicinity of the telephone sta- Fig. 2-. the in-coming alternatingcurrent impulses, after hzfving already passed, it

may be, through an amplifying connection, are transmittedby a translator U to the grid circuit of-a directing amplifier within the anode circuit of which there is arranged .an ohmic resistance W. The voltage for series with the control resistance W within the anode circuit. In this case, the oscilla ting circuit-provided the ohmic resistances and the time-constants of both branches of the circuit are equal-acts after the manner of an ohmic resistance for-continuous current. ln case of resonance, the impedance for by the. formula A v z z where 0. stands for the frequency of the circuit, L for the inductance and R for the ohmic resistance. Hence, the said oscillating circuit acts in the Case of an alternating current like a real. ohmic resistance which, by keeping R low, may beraised to a very high value, so that practically speaking no alternating current can any longeixflow through. In this case, the voltage drop at the control resistance will take place almost instantaneously. Fig. 4 discloses another system of connection; A resistance IV, preferably equal 1n size to the control resistance .lV, is connected up in parallel with the latter, while intermediate the two there is, inserted an os-' cillatingcircuit similar to the one shown in Fig. 8. In this arrangement, the alternating current-even in the case theresistance of the oscillating element is not extraordinarily high for said currentwill take its course almost exclusively through the resistance WV whereas the continuous current will pass in two approximately equal halves through the two ohmic resistances.

l-Vhenever it is a'case of alternating currents of diiferent frequency, such, for example, asa speaking current, then-when employing the system of connection disclosed in Fig. -2a plurality of'such tuning element'combinations L, C will be connected in parallel with each other within alternating current is represented the relay coil or for the displacement of the secondary circuit, as disclosed in Fig. 5, potential at the grid of the speech amplifier so that the'several different frequencies exis derived from the ends of the resistance isting in the several branches, will be dis- ,In accordance with our invention there is tributed over thefrequency range entering provided a shunt to this resistance comprisinto consideration. Again, when making ing the capacity C and the inductance L use of the form of connection shown in Fig. which elements are tuned to the frequency 3, a number of'oscillating circuits, consistof the alternating control current.

In this arrangement, .the alternating cur,- rent passes without encountering any notable. resistance, through the. shunt, whereas owing tothe counter-electromotive force of the inductance and which is at its maximum when the current first begins to flow-the capacity is unable to absorb any appreciable quantity of continuous current. As a' result. the voltage at the control resistance rapidly attains the value required.

In the form of connection disclosed in. Fig. 3, capacity C and inductance L are mg of capacity and inductance, and tunedto different frequencies, will be connected in series within the anode circuit, as illustrated in Fig. 6. This is required for the reason that'the impedance of the circuit will become very much smaller even at -already comparatively slight deviations of the frequency fromthe resonancevalue. The connection shown in Fig. 4 may be proceeded with in exactly the same manner. By

employing suitable selecting connections there is in additionprovided the possibility of selecting a limited frequency area even where a large frequency area'prevails for the alternating control current, and of onlyemploying this said limited area for control purposes. The secondarycircuit may then be operated by aid of a smaller number of oscillating elements.

hat we claim is;

1. In combination, two two-waytelephone lines, a thermionic speech. amplifier for each of said lines, each of said amplifiers comprising a cathode, a: grid, and a plate and having its' grid circuit connected to its own line and its plate circuit connected to the other line, the normal potential of the grid being chosen. such that the speech amplifier is inoperative at that potential, a thermionic directing amplifier for each line having its grid circuit connected therein, an ohmic resistance disposed in the plate circuit of each directing amplifier, each resistance being also disposed in the grid c rcuit, of the ap pertaining speech amplifier, such that when speech is transmitted across said long distance line the voltage drop in saidresistance, caused by the amplified and rectified speech currents flowing inc the plate circuit of the directing amplifier, will increase the prising a cathode, a grid, and a plate and' render the latter operative.

2. In combination, two two-way telephone lines, a thermionic speech amplifier for each of said lines, each of said amplifiers comgrid' potential of said speech amplifier to having its grid vcircuit connected to its own line and its plate circuit connected to the other line, the normal potential of the grid being chosen such that the speech amplifier is inoperative at that potential, a thermiomc directing amplifier for each line, hav-.

ing its grid circuit connected therein, a resistance disposed in the plate circuit of each directing amplifier, each resistance being also disposed in the grid circuit of the appertaining speech amplifier and in the grid circuit ofthe directing amplifier appertaining tothe other long distance line, such that when speech is transmitted across the firstmentioned long distance line, the voltage. drop in said resistance, caused by the rectiof said lines, each of said amplifiers com prising a cathode, a grid, and a plate and having its grid circuit connected to its own lineand its plate circuit connected to the other line, the normal potential of the grid being chosen such that the speech "amplifier .ing amplifier, each resistance being also dis is inoperative at that potential, a thermionic directing amplifier for each line,.hav ing its grid clrcuit connected therein, a-resistance disposed in the plate circuit of each directposed in the grid circuit of the appertaining speech amplifier and in the grid circuit of the directing amplifier appertaining tothe other long distance line, a capacity connected in parallel to each resistance for the purpose of securing a gradual fluctuation of voltage at the ends of'the' resistance'withi'n the plate circuit of the appertaining direct 7 ing amplifier, the voltage drop in .said resistance, when speech currents are influenc ing' the grid of said directing amplifier, serving to increase the grid potential of said speechamplifier soas to render the latter operative and to decrease the grid potential of said directing amplifier appertaining to the other long'distance line so as to render said latter" directing amplifier inoperative.

4;. In combination, two two-way telephone lines, a thermionic speechjamplifier 'for eachof said lines, each ofsaid ampli fiers compris ng a cathode, a grid, and a plate and having its grid circuit connected to its own line and its plate circuit connected to the other line, the normal potential of the grid being chosen such that the speech amplifier is inoperative at that potential, a thermionic directing amplifier for each line, having its grid circuit connected therein, a resistance disposed in the plate circuit of each directing amplifier andeach resistancebeing also disposed in the grid circuit of the appertaining speech amplifier,

and an amplifier foreachidirecting amplifier connected at its output side to the input side of its directing amplifier and atits input side to the appertaining line, said amplifier being adapted to amplify the reversespeaking currents before they pass into the directing amplifier so that this latter is operating with saturation for all alternatingcurrents occurring during the service,

'5. In combination, two two-way telephone lines, a thermionic speech amplifier for each of said lines, each of said amplifiers comprising a cathode, a grid, and a plate and having its grid circuit connected to its own lineand its plate circuit connected to the other line, the normal potential of the grid being chosen such that the speech amplifier isinoperative at that potential, a thermionic directing amplifier for each line, having its grid circuit connected therein, a resistance dlsposed 1n the plate circuit of each directing amplifier, and each resistance being also disposed in the grid circuit "of the appertaining'speech amplifierand'in the grid circuit of the directing amplifier appertaining to the other long distance line,'an oscillatory unit, tuned o,

the frequency of the incoming alternating an ohmic resistance.-

currents and consisting of a capacity and -an inductance, said unit being located adjacent to said resistance and connected into the anode circuit of the directing amplifier, such that the entire combination of the ele- 'ments form-ing the connections for the con-' tinuous current componentof the alternating current rectified, possesses the nature of nected to the other line, the normal potential of the grid being chosen such that the speech amplifier is inoperative at that potential, a thermionic directing amplifier for each line, having its grid circuit connected therein, a resistance disposed in the plate circuit of each directing amplifier, and each resistance being also disposed in the grid circuit of the ap crtaining speech amplifier andin the grid circuit of the directing amplifier appertaining to the other long distance line, an oscillatory unit tuned to the frequency of the incoming alternating currents and consisting of an inductance and a capacity, said unit being disposed in the anode circuit of the directing amplifier and in parallel to said resistance. a

7. In. combination, two two-way tele phonelines, a thermionic speech amplifier or each of said lines, each of said amplifiers comprising a cathode,a grid, and a plate and havingits grid circuit connected nected to the other line, the normal potential of the"grid being chosen such that the speech amplifier is inoperative at that potential, a thermionic directing amplifier for each line, having its grid circuit connected therein, a re'sistance disposed in the plate lifier and in the grid circuit of the directing amplifier appertaining to the other long distance line, a plurality of oscillatory tributed over the frequency range ofthe im- 50' units, whose natural frequencies are discoming speaking currents, the said, units being inserted in the plate circuit of each 4 directing amplifier. i

8. In combination, two two-way telephone lines,"a thermionic speech amplifier for each of said lines, each of said amplifiers comprising a cathode, a-grid, and a plate and ,having its grid circuit connected to its own line and its plate circuit connected to the other line, the normal potential ofv the grid being chosen such that the speech amplifier is inoperative at that potential, a thermionic directing amplifier for each line, having its -grid circuit connected therein, an ohmic resistance disposed in the plate circuit of each directing amplifier,

and each resistance being also disposed in I the grid circuit of the appertaining speech amplifier, such that when speech is trans mitted across a long distance line, the voltage drop in said resistance, caused by the amplified and rectified speech currents flowing inthe plate circuit of the directing amplifier, will increase the potential of said speech-amplifier to render this latter operative, and selective oscillatory units dis-- posed in the anode circuit of the directing amplifier for selecting a definitenarrow frequency range-out of therange of speaking to its own line and. its plate circuit concurrent frequencies for controlling purposes as describe r7 In testimony whereof we afiix our signatunes. 7

BRUNO POHLMANN. ARTHUR ,CLAUSING. 

